In compressor cascade plants or systems, or in compressor booster plants or systems, both with multiple groups of compressors, it is necessary to perform coordination between the different groups of compressors, said different groups of compressors comprising at least one low temperature (LT) compressor and at least one high temperature (MT) compressor. Coordination is necessary when the LT compressor group needs to reject heat, but the MT compressor group is not in operation, i.e., none of the MT compressors are running. If the MT compressors are not running, the LT compressor group cannot reject heat. The LT compressor circuit is operating at lower evaporator temperatures than the evaporator temperatures of the MT compressor circuit.
EP 1 790 919 discloses an aspect directed to a refrigeration system for vapor compression refrigeration cycle including a heat source circuit provided with a high temperature compressor and a utilization circuit connected to the heat source circuit and provided with an evaporator and a low temperature compressor. The refrigeration system includes an operation control means for switching the high temperature compressor between actuated state and suspended state based on a refrigerant suction pressure; and an actuation control means for actuating the low temperature compressor to increase the refrigerant suction pressure in the high temperature compressor when the high temperature compressor is suspended and given conditions including a condition concerning a request for cooling in the evaporator are met. The high temperature compressor is switched between actuated state and suspended state based on the refrigerant suction pressure. In the process of restarting the high temperature compressor in the suspended state, if given conditions including a condition concerning a request for cooling in the evaporator are met, the low temperature compressor is actuated to increase the refrigerant suction pressure in the high temperature compressor.
The high temperature compressor and the low temperature compressor of EP 1 790 919 are connected serially in a one part circuit only, and are not connected in parallel. There is no cooling circuit divided into a low temperature (LT) part of the cooling circuit and having one or more compressors exclusive to the low temperature part, and a high temperature (MT) part of the cooling circuit and having one or more other compressors exclusive to the high temperature part.